Effects of selenium supplementation on glucosinolate biosynthesis in broccoli

Authors: TIAN, MING - Cornell University; Yang, Yong; AVILA, FABRICIO - Cornell University; Fish, Tara; YUAN, HUI - Cornell University; HUI, MAIXIA - Cornell University; PAN, SIYI - Huazhong Agricultural University; Thannhauser, Theodore - Ted; Li, Li

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/5/2018
Publication Date: 7/5/2018
Citation: Tian, M., Yang, Y., Avila, F., Fish, T., Yuan, H., Hui, M., Pan, S., Thannhauser, T.W., Li, L. 2018. Effects of selenium supplementation on glucosinolate biosynthesis in broccoli. Journal of Agricultural and Food Chemistry. 66:8036-8044.

Interpretive Summary: Selenium (Se) is an essential micronutrient for animals and humans, and has other health benefits including being a cancer preventive agent. Some glucosinolate hydrolysis compounds are also known to possess anticancer properties. Broccoli is one of the most nutrient-dense vegetables and contains high levels of glucosinolates. While the beneficial Se-containing compounds can be significantly increased with increased Se dosages, Se treatments can reduce glucosinolate levels. However, the basis by which Se affects glucosinolate levels in broccoli is not very clear. In this study, we examined the effects of Se on total and individual glucosinolate levels in sprouts, young leaves and florets of two broccoli cultivars. We found that the Se supplementation at 25 uM reduces glucosinolate accumulation in broccoli florets and leaves. We showed that the reduction is not associated with plant sulfur nutrition, but is resulted from reduced levels of glucosinolate precursor amino acids and decreased expression of genes associated with the glucosinolate biosynthesis. Comparative proteomics analysis also identified other proteins in some metabolic and cellular processes that are affected by Se treatment. This study provide information for a better understanding of glucosinolate accumulation in response to Se supplement in broccoli.

Technical Abstract: Selenium (Se) enriched broccoli adds health beneficial selenium-containing compounds, but may contain reduced amounts of chemopreventive glucosinolates. To investigate the basis by which Se treatment influences glucosinolate levels, we treated two broccoli cultivars with 25 uM Na2SeO4. We found that the Se supplementation suppressed the accumulation of total glucosinolates, particularly glucoraphanin, the direct precursor for a potent anticancer compound, in broccoli florets and leaves. We showed that the suppression was not associated with plant sulfur nutrition. The levels of glucosinolate precursor’s methionine and phenylalanine as well as the expression of genes in the glucosinolate biosynthesis were greatly decreased following Se supplementation. Comparative proteomic analysis identified proteins in multiple metabolic and cellular processes that were greatly affected and detected an enzyme affecting methionine biosynthesis that was reduced in Se biofortified broccoli. These results indicate that the Se conferred glucosinolate reduction is associated with its negative effects on precursor amino acid biosynthesis and glucosinolate biosynthetic gene expression, and provide information for a better understanding of glucosinolate accumulation in response to Se supplement in broccoli.